In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are used in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified composition is used, which includes a base material component that exhibits a changed solubility in a developing solution under the action of acid and an acid-generator component that generates acid upon exposure.
For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a chemically amplified positive resist which contains, as a base component (base resin), a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator is typically used. If a resist film formed using such a resist composition is selectively exposed at the time of forming a resist pattern, in exposed areas, acid is generated from the acid generator component, and the polarity of the base resin increases by the action of the generated acid, thereby making the exposed areas of the resist film soluble in the alkali developing solution. Thus, by conducting alkali developing, the unexposed portions of the resist film remain to form a positive resist pattern.
On the other hand, when such a base resin is applied to a solvent developing process using a developing solution containing an organic solvent (organic developing solution), the solubility of the exposed portions in an organic developing solution is decreased. As a result, the unexposed portions of the resist film are dissolved and removed by the organic developing solution, and a negative resist pattern in which the exposed portions of the resist film are remaining is formed. Such a solvent developing process for forming a negative-tone resist composition is sometimes referred to as “negative-tone developing process” (for example, see Patent Literature 1).
In general, the base resin used for a chemically amplified resist composition contains a plurality of structural units for improving lithography properties and the like.
For example, in the case of a resin composition which exhibits increased solubility in an alkali developing solution by the action of acid, a structural unit containing an acid decomposable group which is decomposed by the action of acid generated from an acid generator component and exhibits increased polarity. Further, a structural unit containing a lactone-containing cyclic group or a structural unit containing a polar group such as a hydroxy group is used in combination.
Further, in the formation of a resist pattern, the behavior of acid generated from the acid generator component upon exposure is one of the factors which have large influence on the lithography properties.
In consideration of the above, there has been proposed a chemically amplified resist composition which uses, in combination with an acid generator component, an acid diffusion control agent which controls the diffusion of acid generated from the acid generator component upon exposure.
For example, Patent Literature 2 discloses a resist composition including a resin component that exhibits changed solubility in a developing solution by the action of acid, an acid generator component, and a photoreactive quencher as an acid diffusion control agent, wherein the photoreactive quencher has a cation moiety having a specific structure. The photoreactive quencher goes under an ion exchange reaction with the acid generated from the acid generator component to exhibit a quenching effect. By including a photoreactive quencher, acid generated from the acid generator component can be suppressed from being diffused from exposed portions of the resist film to unexposed portions of the resist film. As a result, lithography properties can be improved.